A large proportion (some estimates are as high as twenty-five percent) of the electricity generated in the United States each year goes to lighting. Accordingly, there is an ongoing need to provide lighting fixtures (1) which are easier to install, (2) which reduce the possibility of injury during installation, repair, maintenance, replacement and/or removal, and/or (3) which make it possible for the lighting fixture to be held more securely in place.
In addition, with the growing popularity of lighting elements which include solid state light emitters (e.g., light emitting diodes), there is an increasing demand for lighting fixtures (and components thereof) which facilitate the use of such lighting elements while maximizing the benefits obtained from using such lighting elements and minimizing or eliminating any drawbacks from using such lighting elements.
One example of a conventional recessed light fixture comprises a metal cylinder (“can”) mounted into the ceiling using horizontal metal struts attached to the ceiling joints. Within the cylinder, mounted on an adjustable sliding plate, is light bulb socket into which a light bulb is inserted. Typically a 60 W incandescent light bulb or a 15 W compact fluorescent bulb is used. For example, a conventional recessed light fixture is depicted in FIG. 1.
In this conventional fixture, around the annulus of the bulb and extending downward to the lower inside edge of the cylinder is a baffle or reflecting cone. A cosmetic ring is placed around the bottom edge of the cylinder and extending outward to cover the area immediately surrounding the circular cutout in the ceiling and create an attractive edging around the light output aperture.
The position (height) of the bulb can be set such that the bulb is not directly visible to the people standing in the room and the light from the fixture is directed so that it principally illuminates an area below the fixture.
These fixtures are popular because they do not create significant glare (being recessed) and highlight objects situated below them.
In many cases (e.g., most residential applications), the “cans” are required to be substantially airtight around the sides and top to prevent the loss of ambient heat or cooling from the room into the ceiling cavity through the fixture. As the lamp is mounted in the can, much of the heat generated by the light source is trapped within the can, because the air heated in the can rises and is trapped within the can. Special insulation is usually required around the can within the ceiling cavity to prevent fire.
As indicated above, some aspects of the present inventive subject matter are directed to providing lighting fixtures which are suitable for use with light emitting elements which includes solid state light emitters. The environment inside a conventional can are described above is not ideal for solid-state lighting. LEDs, for example, have significant energy and lifetime benefits over incandescent and fluorescent light sources—LEDs, however, do not operate well in high temperatures. LED light sources have operating lifetimes of decades as opposed to just months or 1-2 years for many incandescent bulbs. An LED's lifetime is significantly shortened, however, if it operates at elevated temperatures. It is generally accepted that the junction temperature of an LED should not exceed 70 degrees C. if a long lifetime is desired.
Efficient individual LED light sources typically provide between 3 and 50 lumens of light per source (LED die or lamp) depending on the size of the LED die. A typical recessed downlight using a 60 W incandescent bulb provides about 500 lumens of light, so it can be seen that to provide a similar amount of light from LEDs, multiple LED light sources would be required.
To provide a similar amount of light using “small die” (typically 300 square micrometers), approximately 200 die would be required, or, alternatively using large “power” die (typically approximately 1 square millimeter) 10-20 die would be required.
For the above and other reasons, efforts have been ongoing to develop ways by which solid state light emitters can be used in place of incandescent lights, fluorescent lights and other light-generating devices in a wide variety of applications. In addition, where light emitting diodes (or other solid state light emitters) are already being used, efforts are ongoing to provide light emitting diodes (or other solid state light emitters) which are improved, e.g., with respect to energy efficiency, color rendering index (CRI Ra), contrast, efficacy (1 m/W), cost and/or duration of service.